This invention relates generally to a temperature control system for an absorption refrigerating apparatus, and more particularly to such a temperature control system which can suitably meet requirements for a large-scale equipment (e.g. an area-wide air-conditioning), such as a quick response to a load change and an improved precision of an outlet temperature.
Generally, for example, an absorption refrigerating apparatus used for an area-wide air-conditioning is utilized in a heat supply business, and therefore in many case the outlet temperature of cold water constitutes a feature from the viewpoint of sales. Therefore, it is required to enhance the precision of the outlet temperature of the supply cold water.
In addition, in this type of absorption refrigerating apparatus, it is expected that a capacity control of a wide range is required, and that a quick response to a load change is required.
Further, in connection with the fleon gas problem recently drawing much attention, it is expected that there will be an increasing demand for process-purpose absorption refrigerating apparatus. The requirements for such a process-purpose refrigerating apparatus are also a quick response to a load change and the precision of the cold water outlet temperature.
Referring to the prior art, there is known a technique of a capacity control in a single absorption refrigerating machine, as disclosed, for example, in Japanese Patent Unexamined Publication No. 57-105659.
More specifically, in this prior art technique, the absorption refrigerating machine comprises an evaporator for evaporating a cooling medium by cold water flowing through a load (e.g. an air-conditioner), an absorber for causing the evaporated cooling medium to be absorbed in a solution, a regenerator for separating the solution, which has absorbed the cooling medium, into the cooling medium and the solution by a heated fluid, a condenser for condensing the cooling medium vapor separated by the regenerator, and a cooling water system for cooling the absorber and the condenser. In this absorption refrigerating machine, the temperature of the cold water cooled by the evaporator is detected by a cold water outlet temperature detector, and when the temperature of the cold water is higher than a set temperature, a signal which increases the degree of opening by an amount proportional to the deviation is sent to a control valve for controlling the flow rate of the heated fluid to be fed to the regenerator. Thus, the cold water temperature is controlled by a so-called proportional control.
The proportional control known as the conventional technique is a simple control as disclosed in the above Japanese Patent Unexamined Publication No. 57-105659, and the proportional control can make the response to the load quicker, but suffers from a problem that the precision of the outlet temperature of the cold water is not so good.
A proportional-plus-integral-plus-derivative control (hereinafter referred to as "PID control") also known as a conventional control achieves a good precision of the cold water outlet temperature; however, in the type of absorption refrigerating machine in which the time constant is long, in order that the cold water outlet temperature will not overshoot a target temperature when activating the refrigerating machine, the PID control is so adjusted as to obtain a relatively slow response, and therefore a problem is encountered in association with the response speed.
However, there has not yet been known any capacity control apparatus or any temperature control system in which two or more controls are performed at the same time with respect to a single refrigerating machine.
There is now an increasing need for a very large-size, highly-efficient absorption refrigerating apparatus, and the manufacturers take the minimum cost into consideration in connection with the production technology, the transportation method and so on. Under such circumstances, it is expected that a so-called system refrigerating apparatus, constituted by a combination of two or more absorption refrigerating machines so as to perform a predetermined refrigerating ability, will become a main stream of very large-size absorption refrigerating apparatus. However, there has not yet been known any particular prior art related to a combination of temperature controls for the plurality of absorption refrigerating machines which are combined together with respect to the flow of the cold water to be circulated at the load side so as to perform a predetermined ability.
In view of such a background, the simultaneous temperature control of two or more refrigerating machines is necessary, and also it is necessary to enhance the precision of the cold water outlet temperature and to increase the response speed.